1. Field of the Invention
The present invention relates to the papermaking arts. More specifically, the present invention relates to seamed fabrics for use with a paper machine. The invention is especially applicable to the production of seams on dryer fabrics, but also may be used for forming fabrics, press fabrics and other industrial fabrics/belts that utilize a spiral seam.
2. Description of the Related Art
During the papermaking process, a cellulosic fibrous web is formed by depositing a fibrous slurry, that is, an aqueous dispersion of cellulose fibers, onto a moving forming fabric in the forming section of a paper machine. A large amount of water is drained from the slurry through the forming fabric, leaving the cellulosic fibrous web on the surface of the forming fabric.
The newly formed cellulosic fibrous web proceeds from the forming section to a press section, which includes a series of press nips. The cellulosic fibrous web passes through the press nips supported by a press fabric, or, as is often the case, between two such press fabrics. In the press nips, the cellulosic fibrous web is subjected to compressive forces which squeeze water therefrom, and which adhere the cellulosic fibers in the web to one another to turn the cellulosic fibrous web into a paper sheet. The water is accepted by the press fabric or fabrics and, ideally, does not return to the paper sheet.
The paper sheet finally proceeds to a dryer section, which includes at least one series of rotatable dryer drums or cylinders, which are internally heated by steam. The newly formed paper sheet is directed in a serpentine path sequentially around each in the series of drums by a dryer fabric, which holds the paper sheet closely against the surfaces of the drums. The heated drums reduce the water content of the paper sheet to a desirable level through evaporation.
It should be appreciated that the forming, press and dryer fabrics all take the form of endless loops on the paper machine and function in the manner of conveyors. It should further be appreciated that paper manufacture is a continuous process which proceeds at considerable speeds. That is to say, the fibrous slurry is continuously deposited onto the forming fabric in the forming section, while a newly manufactured paper sheet is continuously wound onto rolls after it exits from the dryer section.
Woven fabrics take many different forms. For example, they may be woven endless, or flat woven and subsequently rendered into endless form with a seam. Woven fabrics are typically in the form of endless loops, or are seamable into such forms, having a specific length, measured longitudinally therearound, and a specific width, measured transversely thereacross. Because paper machine configurations vary widely, paper machine clothing manufacturers are required to produce fabrics, and other paper machine clothing, to the dimensions required to fit particular positions in the paper machines of their customers. Needless to say, this requirement makes it difficult to streamline the manufacturing process, as each fabric must typically be made to order.
Fabrics in modern papermaking machines may have a width of from 5 to over 33 feet, a length of from 40 to over 400 feet and weigh from approximately 100 to over 3,000 pounds. These fabrics wear out and require replacement. Replacement of fabrics often involves taking the machine out of service, removing the worn fabric, setting up to install a fabric and installing the new fabric. Because of the solid support beams for dryer sections, all dryer fabrics must have a seam. Installation of the fabric includes pulling the fabric body onto a machine and joining the fabric ends to form an endless belt.
The seam region of any workable fabric must behave in use as close to the body of the fabric in order to prevent the periodic marking by the seam region of the paper product being manufactured.
To facilitate seaming, many current fabrics have seaming loops on the crosswise edges of the two ends of the fabric. The seaming loops themselves are formed by the machine-direction (MD) yarns of the fabric. A seam is formed by bringing the two ends of the fabric press together, by interdigitating the seaming loops at the two ends of the fabric, and by directing a so-called pin, or pintle, through the passage defined by the interdigitated seaming loops to lock the two ends of the fabric together.
Alternatively, a monofilament seaming spiral may be attached to the seaming loops at each of the two ends of the papermaker's fabric. The monofilament seaming spirals are connected to the seaming loops by at least one connecting yarn. The coils of the spirals at the two ends of the fabric may again then be interdigitated and joined to one another on the paper machine to form a seam usually referred to as a spiral seam.
In a so-called warp loop seam, the rows of loops are formed of extended edge loops of warp yarns in the fabric structure of the fabric. In a spiral seam, each row of loops is instead formed of a separate, preformed yarn spiral, which is extended along and attached by means of a CD pintle connecting the spiral, intermeshed with the machine direction yarns, such as warp yarns, to the seam edge of the fabric. The coils of the spirals at the two ends of the fabric may again then be interdigitated and joined to one another on the paper machine to form a seam usually referred to as a spiral seam. Alternatively, the spiral can be attached to the clothing by a number of cross-machine direction yarns being raveled a distance from the seam edge, whereupon the loops of the spiral are inserted into the thus formed looser edge portion. Then the edge is folded back over itself and is attached to the clothing, for instance, by using a sewing machine. Independently of how the spiral is attached, the clothing comprises two spirals, one along each seam edge, which, when joining together the fabric, are meshed with each other like a zipper so as to be joined together by means of a pintle wire or the like.
Alternatively, fabrics can be formed completely of spirals as taught by Gauthier, U.S. Pat. No. 4,567,077; which is incorporated herein by reference. In this case, the spirals are connected to each other by at least one connecting pin. In theory, the seam can therefore be at any location in the fabric body where a connecting pin may be removed. The best known advantage of a spiral fabric versus a woven fabric is the seam is geometrically similar to the fabric body.
A seam is generally a critical part of a seamed fabric, since uniform paper quality, low marking and excellent runnability of the fabric are required.
An important aspect of seaming a fabric on a paper machine is the necessity of threading a leader wire, pin or pintle through the fabric loops or spirals on the opposed ends of the fabric. The ends of the fabric must be brought together on the machine, and a flexible leader wire is threaded through the loops or spirals. Preferably, the leader wire can be threaded across in one operation. Frequently, however, only a short section or length is done at a time. Then it is used to pull the pintle through while pulling the leader out of a gap between loops. This is repeated across the width of the machine, which may exceed 400 inches. This process is made difficult because the leader wire or pintle tends to pop out or migrate out of the loops. When this migration occurs the leader wire or pintle must be removed and the threading process restarted, thus increasing the time to seam the fabric. Also, since the seaming spirals are opaque, it is impossible to visually follow the progressing leader wire through the seam.
Therefore, during a seaming operation, a need exists to reduce migration of the leader wire or pintle and to facilitate the insertion thereof. The present invention provides a solution to this problem.